Can someone help me to get buffered reader to work in Java?

问题

Here I am trying to read a document that has words and corresponding abbreviations. E.g.

one,1
two,2
easy,ez

Each line is separated, and the words are separated from the abbreviations with a comma.

When I want the buffered reader to keep reading lines using

while ((line = br.readLine()) != null)

it won't. It will only read the first line. This means it will display the abbreviation for one, which is 1. But if I input another value say two, I get this error message.

Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: 5
    at java.lang.String.charAt(String.java:658)
    at shortener.NewClass.Short(NewClass.java:41)
    at shortener.NewClass.main(NewClass.java:26)
Java Result:

here's the code

public static String Short(String input) {

    try {
        FileReader fr = new FileReader("abbreviations.txt");
        BufferedReader br = new BufferedReader(fr);

        String line;
        while ((line = br.readLine()) != null) {

            for(int i = 0; i <= line.length(); i++) {
                if(line.charAt(i) == ','){
                    String strOrig = line.substring(0, i);
                    if(strOrig.equals(input)) {
                        String strAbv = line.substring(line.length()-1);
                        return strAbv;
                        }
                    }                
                }
            }   
        br.close();
        } catch (IOException e) {
        out.println("File Not found");
    }
    return null;
}

回答1:

You have made the conditional expression in for loop as i lesser than or equal to line.length(). That's wrong.i shouldn't be equal to the length of the line. Change this

for(int i = 0; i <= line.length(); i++)

for(int i = 0; i < line.length(); i++)

you can't make i equal to the length of line. The index starts from 0. so, the valid indexes would be from 0 to length-1

回答2:

This is incorrect:

for(int i = 0; i <= line.length(); i++) {

as it is accessing one too many. To correct:

for(int i = 0; i < line.length(); i++) {

Note that the posted code does not close() the reader if the abbreviation is found. Use a finally block or try-with-resources statement to ensue the reader is closed.

Other:

String.split() could be used to separate the line into two tokens instead of explicitly coding the separation.

A Properties style file could be used to store the abbreviation-to-term map instead of a comma separated file. The Properties class provides a mechanism for loading the file and methods for searching the map:

   // If the 'abbreviations.txt' file is not updated
   // by the program then arrange for it to be loaded once.
   //
   try (final FileInputStream is =
            new FileInputStream("abbreviations.txt"))
   {
       final Properties p = new Properties();
       p.load(is);
       return p.getProperty(input);
   }

回答3:

Check out the for loop part of your code:

for(int i = 0; i <= line.length(); i++) {

It should be changed to this:

for(int i = 0; i < line.length(); i++) {

Notice how <= was changed to <:

for(int i = 0; i <= line.length(); i++) {
//vs:
for(int i = 0; i < line.length(); i++) {

For pretty much all coding, including java, counting starts at 0. So where you would normally say 5, in coding you would say 4.

Let's say the length of the array is 3, meaning it contains 0, 1, and 2. So, when doing this:

for(int i = 0; i <= line.length(); i++) {
//length of the line is 3, so:
for(int i = 0; i <= 3; i++) {

now, it will loop threw the numbers 0, 1, 2, and 3. Yet, the line is only contains only 0, 1, and 2. So, if we were to do this:

for(int i = 0; i < line.length(); i++) {
//length of the line is 3, so:
for(int i = 0; i < 3; i++) {

Using this new code, it will loop threw 0, 1, and 2, the same length of our line, 0, 1, and 2.

来源：https://stackoverflow.com/questions/22840689/can-someone-help-me-to-get-buffered-reader-to-work-in-java

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java

bufferedreader